The present invention relates to a method for producing gallium nitride light emitting diode wafer and more particularly pertains to a method for improving the performance of P-type ohmic contact of gallium nitride light emitting diode wafer.
Gallium nitride light emitting diode is a light emitting diode of ultra high brightness. It is widely used in sectors such as communications, transportation and displays as it has the features of being energy-saving, pollution-free, durable, small in size and producing shape colors. In recent years, a large volume of research work has been conducted on the development and improvement of P-type ohmic contacts of light emitting diodes with many structures being invented which basically satisfy the requirements for a functional device. For a conventional P-type ohmic contact of light emitting diode wafer, electron-beam evaporation apparatus is usually used to deposit on the surface of an epitaxial wafer one or more layers of high work function metal. For example, nickel metal is deposited by the electron beam positive deposition and then a layer of conductive metal such as gold is deposited by way of the same method, and finally alloy treatment is applied in order to reduce contact impedance. Gold is the most commonly used material for electrodes, but it has a poor thermal stability at the temperature of 500 degree Celsius or above. Accordingly, this method can reduce contact impedance but is unfavourable to the traverse of electric current on the contact surface and the inside of the wafer. This causes heat emission owing to localized surge of electric current, thereby reducing luminous efficiency of the wafer. Rapid treatment of heat is a relatively effective method in achieving good outward appearance and low contact resistivity. More advanced laser and infrared methods of heat treatment has been developed in recent years which provide better ohmic contacts. However, with the miniaturization and integration of devices, there are even more stringent requirements on the stability and reliability of ohmic contacts of gallium nitride light emitting diodes.